Adjustable valve train with hydraulic lifters

ABSTRACT

A valve train with a hydraulic lifter in an engine, and a method of configuring a hydraulic lifter of an engine, are disclosed. The valve train includes a valve, a cam, and at least one coupling component. The valve train further includes the hydraulic lifter, which has a nominal length and is coupled at least indirectly between the valve and the cam by way of the at least one coupling component. The valve train additionally includes a mechanism for varying the nominal length of the hydraulic lifter so that the nominal length is substantially closer to a minimum length of the hydraulic lifter than to a maximum length of the hydraulic lifter.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a utility patent application which is based on and claims the benefit of U.S. provisional patent application 60/452,778 filed Mar. 7, 2003 and entitled “Adjustable Valve Train With Hydraulic Lifters”.

FIELD OF THE INVENTION

[0002] The present invention relates to internal combustion engines and, more particularly, relates to internal combustion engines in which one or more hydraulic lifters are employed in connection with one or more valve trains of the engines.

BACKGROUND OF THE INVENTION

[0003] Internal combustion engines commonly employ valves that open and close to allow fuel/air mixture to flow into the cylinder(s) of the engine and to allow exhaust to flow out of the cylinder(s). The opening and closing of the valves often is driven by way of one or more rotating cams. Typically, the valves are not driven directly by the cams, but rather are driven by components of valve trains, which in turn are driven by the cams.

[0004] The valve trains of internal combustion engines can take many different forms. For example, commonly, the valves are connected, by way of valve stems associated with those valves, to first ends of rocker arms that are rotatably coupled to the cylinder head. In engines where the cams are located close to the engine crankcase and crankshaft, second ends of the rocker arms can in turn be driven by way of push rods and other linking components that are positioned between the cams and the second ends of the rocker arms. In other engines employing cams that are located near the cylinder head (e.g., “overhead cam” engines), the second ends of the rocker arms themselves can be driven by the cams.

[0005] In many engines having various types of valve trains, one or more hydraulic lifters (also known as “hydraulic tappets” or “hydraulic lash adjusters”) are employed at points along the valve trains. For example, a hydraulic lifter can be employed between a cam (or cam follower riding on the cam) and a push rod connected to a rocker arm. Also for example, a hydraulic lifter can be employed between a rocker arm and a valve stem of a valve. Such hydraulic lifters are employed to compensate for lash that can arise in the valve trains of the engines, for example, lash that arises due to slight changes in the lengths of valve train components such as push rods due to changes in engine operating temperature.

[0006] To ensure quiet and reliable operation of a hydraulic lifter, it is important that an adequate supply of oil be provided to low and high pressure reservoirs with the lifter at all times. A problem often encountered is that, during engine shutdown periods, oil will leak or drain from the reservoirs of its hydraulic lifter(s). Upon subsequent startup of the engine, at least the high pressure reservoirs, and perhaps also the low pressure reservoirs, of the hydraulic lifters can be depleted of oil and largely contain air. Consequently, the hydraulic lifters can compress too readily and too far, and as a result produce lash in the valve trains. This in turn can result in undesirable noise or improper valve timing, at least temporarily, as well as result in damage to components of the valve train (including the lifters themselves). To the extent that collapsed hydraulic lifters can lead to changes in valve event timing, this can also negatively impact other characteristics of engine performance such as engine emissions.

[0007] These problems associated with hydraulic lifters are further compounded in engines that employ automatic compression release (ACR) mechanisms. As known to those of ordinary skill in the art, such mechanisms typically include a component, actuated based upon engine speed, that varies a portion of the surface of the cam. When engine speeds are low, such as during the starting of the engine, a protrusion or bump is created on the base of the cam that causes the hydraulic lifter to move radially outward away from the axis of the cam when the lifter encounters the bump. The bump and cam are positioned such that the movement of the lifter in turn causes the exhaust valve to open slightly during the compression stroke of the engine, which facilitates the starting of the engine. Further, when engine speeds are higher, such as during normal operation of the engine, the bump is eliminated, so that the exhaust valve remains closed during the compression stroke of the engine, thereby maximizing engine power.

[0008] Because the primary effect of an ACR mechanism, namely the opening of the exhaust valve during the compression stroke while the engine is being started, can only be achieved if the valve train communicates to the valve the increase in radial size of the cam occurring due to the bump, it is important that any hydraulic lifter in the valve train be properly pressurized when this is occurring. Yet, as discussed above, the depletion of oil from hydraulic lifters and resulting lash is often greatest at this very time when the engine is being started. Thus, the use of hydraulic lifters in engines employing ACR mechanisms can be especially problematic.

[0009] Given these problems associated with the use of hydraulic lifters in engines, particularly engines employing ACR mechanisms, various attempts have been made to develop methods and mechanisms that prevent or reduce the depletion of oil from hydraulic lifters while an engine is shut down and/or as it is started up, or at least reduce the negative effects of the depletion of oil However, each of these conventional methods and mechanisms has its own disadvantages.

[0010] For example, one existing method is to allow the stack-up tolerances of the valve train to dictate the amount that a hydraulic lifter can bleed out. However, this typically entails a relatively wide and random distribution, leading to substantial variation from engine to engine and start to start in the amount of ACR function as the amount of hydraulic lifter bleed out varies. Such variation in ACR function leads to variation in the starting performance of the engine, which is undesirable.

[0011] A second conventional method involves utilizing a hydraulic lifter that simply does not bleed out its oil. This can be achieved by way of using sealed hydraulic lifters such as those discussed in U.S. Pat. No. 4,574,750 and entitled “Self-Contained Hydraulic Lifter”. However, hydraulic lifters such as those constructed in accordance with this patent are more complex and costly than traditional hydraulic lifters. Further, hydraulic lifters such as those discussed in this patent can be less durable than traditional hydraulic lifers due to their reliance on a flexible membrane material.

[0012] A third conventional method of preventing/reducing hydraulic lifter bleed out involves designing the lubrication system of the engine to include reservoirs and/or valves or anti-siphon features. However, these features also can add significant complexity and cost to engine components, particularly the cylinder head and/or crankcase.

[0013] Therefore, it would be advantageous if a new method or mechanism could be devised that reduced the degree to which an engine's performance suffered due to the depletion of oil from hydraulic lifters, particularly when the engine was first being started. It would in particular be advantageous if such new method or mechanism limited the degree to which the performance of ACR mechanism(s) in an engine were negatively impacted by the depletion of oil from hydraulic lifters. Further, it would be advantageous if such new method or mechanism did not require complicated or costly hydraulic lifter designs or other engine parts and affected engine operation in a relatively consistent manner.

SUMMARY OF THE INVENTION

[0014] The present inventors have recognized that an adjustable valve train (AVT) can be employed to reduce the amount of lash that can occur due to depletion of oil from the hydraulic lifter(s) of the valve train, and consequently can be employed to reduce the negative effects of such lash including, for example, inconsistent automatic compression release (ACR) function. In particular, the use of the AVT makes it possible to set the hydraulic lifter's nominal running length to a length that is significantly less (e.g., more-contracted) than a conventional setting midway between the lifter's greatest (most-expanded) and least (most-contracted) lengths. Consequently, the amount the lifter can shorten when it bleeds out is reduced such that adequate ACR function continues even when the lifter is collapsed, and such that other negative consequences of oil depletion that might otherwise occur including undesirable noise, improper valve timing and possible damage to valve train components are reduced. The present invention is applicable to all valve trains with hydraulic elements (lifters, tappets, adjusters, etc.), including but not limited to those that also have an ACR mechanism.

[0015] In particular, the present invention relates to a valve train in an engine, where the valve train includes a valve, a cam, and at least one coupling component. The valve train further includes a hydraulic lifter having a nominal length and coupled at least indirectly between the valve and the cam by way of the at least one coupling component. The valve train additionally includes a mechanism for varying the nominal length of the hydraulic lifter so that-the nominal length is substantially closer to a minimum length of the hydraulic lifter than to a maximum length of the hydraulic lifter.

[0016] The present invention additionally relates to an internal combustion engine that includes a crankcase, a crankshaft supported by the crankcase, and a camshaft having a cam, where the camshaft is supported by the crankcase and is rotationally coupled to the crankshaft so that rotation of the crankshaft causes rotation of the camshaft. The internal combustion engine further includes a valve, and at least one component coupling the valve to the cam, where the at least one component includes a hydraulic lifter. The internal combustion engine additionally includes a mechanism for adjusting a nominal position associated with the hydraulic lifter so that the nominal position is closer to a first position at which the hydraulic lifter is at a minimum length than to a second position at which the hydraulic lifter is at a maximum length.

[0017] The present invention further relates to a method of configuring a hydraulic lifter of an internal combustion engine. The method includes providing a valve train including the hydraulic lifter, where the valve train couples a cam of the engine to a valve of the engine at least indirectly by way of the hydraulic lifter. The method also includes adjusting at least one component of the valve train to set a nominal length of the hydraulic lifter so that the nominal length is substantially closer to a minimum length of the hydraulic lifter than a maximum length of the hydraulic lifter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a perspective view of an exemplary internal combustion engine in which adjustable valve trains with hydraulic lifters in accordance with certain embodiments of the present invention are implemented;

[0019]FIG. 2 is a cross-sectional view of an exemplary adjustable valve train including a hydraulic lifter that can be implemented in the engine of FIG. 1, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Referring to FIG. 1, a perspective view of an exemplary internal combustion engine in which some embodiments of the present invention could be implemented is shown to be a single-cylinder, vertical-crankshaft “Command Single” internal combustion engine 10 designed by Kohler Co. of Kohler, Wis. As with many other internal combustion engines, the engine 10 includes a crankcase 12 and a blower housing 14, inside of which are a fan 16 and a flywheel (not shown). The engine 10 further includes a starter 18, a cylinder 20, a cylinder head 22 (which includes air intake and exhaust ports, not shown), and a rocker arm cover 24. As is well known in the art, during operation of the engine 10, a piston (not shown) moves back and forth within the cylinder 20 towards and away from the cylinder head 22. The movement of the piston in turn causes rotation of a vertically-oriented crankshaft 26, as well as rotation of the fan 16 and the flywheel, which are coupled to the crankshaft.

[0021] Although the embodiment shown in FIG. 1 is a single cylinder, vertical-crankshaft internal combustion engine, the present invention is further applicable to any internal combustion or other type of engine having one or more valve trains in which one or more hydraulic lifters are employed. Thus, the present invention is intended to be applicable to a variety of internal combustion engines and other engines, including diesel engines and engines employed in compressor systems, etc., engines having two or more cylinders, and engines having horizontally or vertically-oriented crankshafts.

[0022] Turning to FIG. 2, components of an exemplary adjustable valve train (AVT) 30 of the engine 10 are shown in cross-section. The adjustable valve train 30 in particular includes a cam 32 on a camshaft 34, which is typically driven by the crankshaft 26 (typically indirectly, e.g., by way of gear(s) or a belt). Additionally, the valve train 30 includes a valve 44. The valve 44 includes a valve stem portion 46 and a valve head portion 48. The opening and closing of the valve head portion 48 governs whether fuel/air mixture or exhaust can enter or exit the cylinder 20 (depending upon whether the valve is an intake or exhaust valve, respectively).

[0023] Linking the valve 44 with the cam 32 are a series of additional components of the adjustable valve train 30. In particular, these additional components include a hydraulic lifter 50, a push rod 52, and a rocker arm 54. As shown in FIG. 2, a first end 56 of the rocker arm 54 engages the valve stem portion 46 and a second end 58 of the rocker arm is coupled to a first end 60 the push rod 52. A second end 62 of the push rod 52 in turn is rotatably or otherwise coupled to a first end 64 of the hydraulic lifter 50, a second end 66 of which rides on the cam 32. The rocker arm 54 is rotatably supported in relation to the cylinder head 22 by way of a stud 100 as discussed further below.

[0024] In alternate embodiments, the components of the adjustable valve train 30, particularly the additional components between the valve 44 and the cam 32, can vary from those shown in FIG. 2. For example, rather than riding directly on the cam, the hydraulic lifter instead could ride directly or indirectly upon a cam follower (not shown) that in turn rode upon the cam. Also, for example, the hydraulic lifter could be at a different location along the valve train 30, such as between the push rod and the rocker arm rather than between the push rod and the cam. Additionally, while the embodiment shown in FIGS. 1 and 2 is of an overhead valve (OHV) internal combustion engine in which the cam and camshaft are positioned proximate the crankcase, the present invention is further applicable to engines having different valve train configurations with hydraulic lifters, such as overhead cam (OHC) engines in which the cam is positioned proximate the cylinder head, or valve-in-block (VIB) engines where the valves are located in the engine block rather than the cylinder head.

[0025] In the present embodiment, the cam 32 includes not only a base circular portion 36 having a constant radius 38 but also a fixed lobe 40 extending outward beyond that radius. Additionally, the cam 32 also includes a retractable protrusion or bump 42 that is shown, in FIG. 2, to protrude outward away from the base circular portion 36 opposite the fixed lobe 40. Whether the bump 42 protrudes outward or, instead, is retracted partly or entirely inward so that it does not extend beyond the radius 38 of the base circular portion 36, is governed by the operation of an automatic compression release (ACR) mechanism (not shown) of which the retractable bump forms a part. As discussed above, the ACR mechanism can take any of a variety of forms as known to those of ordinary skill in the art. Typically, the ACR mechanism is configured to operate so that the bump 42 protrudes outward when the engine is operating at slow speeds (e.g., the engine is just starting operation), and then is retracted as the engine achieves normal operating speed.

[0026] Further as shown in FIG. 2 the hydraulic lifter 50 is of a conventional design and includes an outer cup portion 68 in which is situated an inner plunger portion 70. More specifically, the outer cup portion 68 includes at the lifter's second end 66 a foot 72, which rides on the cam 32, and the inner plunger portion 70 includes an outer end 74 that is connected to/in contact with the second end 62 of the push rod 52. The relative positions of the outer cup portion 68 and the inner plunger portion 70, which is capable of slidable movement into and out of the outer cup portion, are governed not only by the interaction of the hydraulic lifter 50 with external components of the valve train 30 such as the cam 32 and push rod 52, but also by relative oil pressures within first and second chambers 76 and 78, respectively, of the lifter and a spring 80 positioned between the two portions of the lifter.

[0027] In particular, the first chamber 76 is a low-pressure chamber within the inner plunger portion 70 that is fed with oil (or other lubricant) by way of a first oil channel 81 extending through a side wall of the inner plunger portion. The oil is provided to the first oil hole 81 from an inner groove 82 formed between the outer cup portion 68 and the inner plunger portion 70. The inner groove 82 in turn is fed with oil from an outside source (not shown) by way of a second oil channel 84 extending through a side wall of the outer cup portion 68. Additionally, the second chamber 78 is a high-pressure chamber formed between an inner end 86 of the inner plunger portion 70 and the interior of the outer cup portion 68. The spring 80 is contained within the second chamber 78.

[0028] A check valve 88 within the inner end 86 of the inner plunger portion 70 allows oil to flow in only one direction, namely, from the first chamber 76 to the second chamber 78. Oil flows from the first chamber 76 to the second chamber 78 in particular when the pressure placed upon the hydraulic lifter 50 between the push rod 52 and the cam 32 tends to diminish, for example, when the cam turns so that the fixed lobe 40 moves past the lifter and the lifter comes into contact with the base circular portion 36 of the cam. As the foot 72 of the lifter 50 again begins to be pushed away from the central axis of the cam 32 (either due to the fixed lobe 40 or the bump 42), the check valve 88 prevents oil from flowing from the second chamber 78 back into the first chamber 76. To the extent that oil leaves the second chamber 78, it does so by flowing through narrow clearances between the inner plunger portion 70 and the outer cup portion 68.

[0029] As shown, the inner plunger portion 70 of the hydraulic lifter 50 can take on a variety of positions within a range of motion 90 in relation to the outer cup portion 68, the range of motion being shown in FIG. 2 in relation to a shoulder 92 existing along the inner surface of the outer cup portion 68. The range of motion 90 is determined, in the case of the lifter shown in FIG. 2, by the shoulder 92, which limits movement of the inner plunger portion 70 into the outer cup portion 68 and thus limits the lifter's contraction, and by a ridge 94, which limits movement of the inner plunger portion outward away from the outer cup portion and thus limits the lifter's expansion. The relative positions of the inner plunger portion 70 and the outer cup portion 68 determine an overall length 108 of the hydraulic lifter 50.

[0030] When implemented in relation to the adjustable valve train 30, the inner plunger portion 70 has a nominal position relative to the outer plunger portion 68 such that the lifter has a nominal length. This nominal position/length are set such that the valve train 30 has no lash. Although the overall length 108 of the hydraulic lifter 50 and the relative positions of the inner plunger portion 70 and outer cup portion 68 vary slightly (e.g., by a couple thousandths of an inch) from the nominal length and nominal position, respectively, as the cam 32 rotates during operation of the engine 10, more significant variations from the nominal length/position only occur for certain other reasons. In particular, more significant variations from the nominal length/position typically only occur (1) to compensate for lash that can arise in the valve train 30 due to variations in engine operating temperature and corresponding expansion/contraction of one or more of the valve train's components, (2) to compensate for lash that can occur due to wear and tear affecting one or more of the valve train's components over time, and (3) as a result of oil depletion while the engine is shut off. In conventional systems employing a single-setting (non-adjustable) valve train, the inner plunger portion 70 would have a conventional nominal position that is at a first distance 96 away from its most contracted position, where the first distance is about 50% of the range of motion 90 of the inner plunger portion. In other words, a conventional nominal length of a hydraulic lifter in a conventional system is at about midway between the lifter's maximum and minimum lengths.

[0031] In contrast to such conventional systems and in accordance with the present invention, the valve train 30 is an adjustable valve train in which one or more position settings of one or more of the valve train's components can be varied. In particular, in the embodiment shown in FIG. 2, the position of the rocker arm 54 in relation to the cylinder head 22 (and consequently in relation to the cam 32) can be varied. As shown, the rocker arm 54 is mounted on a pivot 98 of the stud 100, which in turn is driven into and supported by the cylinder head 22 (see FIG. 1). The position of the pivot 98 and consequently the rocker arm 54 in relation to the remainder of the stud 100 can be set by varying the position of a threaded adjustment nut 102 in relation to the stud and then locking the position of the adjustment nut by way of a set screw 104.

[0032] More specifically, the adjustment nut 102 and set screw 104 limit movement of the pivot 98 away from the cylinder head 22. Movement of the pivot 98 toward the cylinder head 22 is prevented by the rocker arm 54 itself, which is forced toward the pivot and away from the cylinder head due to pressure provided by a valve spring (not shown) tending to close the valve 44 and due to pressure provided by the hydraulic lifter 50 by way of the push rod 52.

[0033] Further in accordance with the present invention, and through the use of the adjustable valve train 30, the nominal position/length of the hydraulic lifter 50 is modified from the conventional nominal position/length associated with the first distance 96. In particular, the adjustable valve train 30 is set to modify an effective length of the valve train (e.g., the distance between the valve 44 and the cam 32), which in turn varies the length that the lifter should take on to eliminate lash in the valve train. Consequently, the inner plunger portion 70 takes on a modified nominal position that is a second distance 106 away from its most contracted position, where the second distance is significantly less than the first distance 96. Correspondingly, the modified nominal length of the hydraulic lifter is significantly closer to the lifter's minimum length than to the lifter's maximum length.

[0034] The exact setting of the modified nominal position/length of the hydraulic lifter 50 will usually be determined based upon knowledge of intended engine operating conditions. For example, in particular with respect to the embodiment shown in FIG. 2, the second distance 106 is 20% of the overall range of motion 90, such that the nominal length (which is the overall length 108 shown) of the hydraulic lifter 50 is only {fraction (2/10)} of the way from the lifter's minimum length to its maximum length. In other embodiments, the second distance 106 is 10% or 3% of the overall range of motion. In further embodiments, the second distance 106 can be a third of, or less than a third of, the overall range of motion 90 of the inner plunger portion 70 relative to the outer cup portion 68. Correspondingly, the nominal length of the hydraulic lifter 50 can be reduced so that it is twice as close to its minimum length than to its maximum length, or closer. In terms of actual physical size, the second distance 106 also depends upon the embodiment. For example, in some embodiments in which the second distance 106 is 3% of the overall range of motion, the actual physical distance can be on the order of five-to-ten thousandths of an inch.

[0035] Although the size of the second distance 106 (and, correspondingly, the nominal position of the inner plunger portion 70 relative to the outer cup portion 68 and the nominal length of the hydraulic lifter 50) can vary considerably depending upon the embodiment, it is set in a variety of situations to satisfy the same overall goals. In particular, the nominal position/length of the hydraulic lifter 50 is set, using the adjustable valve train 30, so that the lifter is sufficiently contracted that the negative effects associated with possible excessive depletion of oil from the hydraulic lifter are reduced. As discussed above, these negative effects can include improper functioning of ACR mechanism(s) in engines that employ such mechanisms, undesirable noise, undesirable wear and tear on the hydraulic lifter and other parts of the valve train 30, and improper valve timing (and related improper engine operation) that otherwise might occur due to the oil depletion and consequent excessive compressibility of the hydraulic lifter are prevented or at least ameliorated.

[0036] In particular, in the case of engines that employ ACR mechanism(s), the nominal position/length of the hydraulic lifter 50 should be set so that proper (or satisfactory) operation of the ACR mechanism is maintained even when the hydraulic lifter can become bled-out, such as when the engine 10 is started. Thus, in such engines, the nominal position/length of the hydraulic lifter 50 should be set so that the second distance 106 is less (usually significantly less) than the extent to which the ACR bump 42 extends outward from the base circular portion 36 of the cam 32. By setting the hydraulic lifter 50 in this manner, the hydraulic lifter when bled-out will only be able to shorten a small distance when force is applied to the hydraulic lifter (despite the high compressibility of any air within the lifter), and consequently the lifter will still transmit movement to the push rod 52 when it encounters the ACR bump 42.

[0037] At the same time, the setting of the nominal position/length of the hydraulic lifter 50 is not so contracted as to prevent the hydraulic lifter from responding in its usual manner to anticipated engine operating conditions. In particular, the nominal position/length of the hydraulic lifter 50 should not be set to such a contracted level that it is incapable of contracting sufficiently to account for expansion in other components of the valve train as the engine heats up. In most circumstances, such an inability of the hydraulic lifter 50 to contract sufficiently is not of great concern in setting the nominal position/length of the lifter, and consequently the more-contracted settings of the nominal position/length discussed above (e.g., a 3% setting) are appropriate. However, in certain circumstances (e.g., operation of an engine at very low temperatures), it may be appropriate to set the nominal position to a more-expanded level such as the 20% level or even a higher level.

[0038] Although the adjustable valve train 30 shown in FIG. 2 is adjusted by way of the adjustment nut 102/set screw 104 on the stud 100, the present invention is intended to encompass a variety of other adjustable valve trains and lash adjustment mechanisms (not shown by the FIGS.), by which the nominal position(s)/length(s) of hydraulic lifter(s) of an engine can be set and modified. For example, while the nominal position/length of the hydraulic lifter 50 of FIG. 2 can be adjusted by varying the height of the pivot 98 using the adjustment nut 102, it also could be adjusted by varying the orientation, length or other characteristics of the push rod side of the rocker arm or the valve side of the rocker arm, changing the push rod's length, varying the length of the valve stem, varying a characteristic of a cam follower (not shown), etc. Also, in alternate embodiments, the set screw and adjustment nut shown in FIG. 2 could be replaced with other setting adjustment mechanisms. While the present invention is applicable to systems that employ hydraulic lifters (or tappets, lash adjusters, etc.), the present invention is equally applicable to other similar devices.

[0039] The present invention is applicable both to systems that employ ACR mechanisms such as that shown in FIG. 2, as well as to other systems that employ cams or similar actuators (or bumps or other features on the cams or similar actuators) to vary or govern valve/engine performance including, for example, systems providing variable valve timing and standard cams governing normal intended valve motion. In general, the present invention is intended to encompass a variety of embodiments in which one or more adjustable valve train components are adjusted to compensate for unintended or undesired valve train lash (e.g., undesired slack within the valve train) arising due to one or more components within the valve train. The present invention is further intended to encompass embodiments in which one or more adjustable valve train components are capable of being adjusted automatically (e.g., by way of computerized controller(s) and actuator(s)) to adjust nominal length/position of a hydraulic lifter to respond to different operational conditions (e.g., to vary the nominal length/position as engine temperature varies).

[0040] While the foregoing specification illustrates and describes the preferred embodiments of this invention, it is to be understood that the invention is not limited to the precise construction herein disclosed. The invention can be embodied in other specific forms without departing from the spirit or essential attributes of the invention. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention. 

What is claimed is:
 1. A valve train in an engine comprising: a valve; a cam; at least one coupling component; a hydraulic lifter having a nominal length and coupled at least indirectly between the valve and the cam by way of the at least one coupling component; and a mechanism for varying the nominal length of the hydraulic lifter so that the nominal length is substantially closer to a minimum length of the hydraulic lifter than to a maximum length of the hydraulic lifter.
 2. The valve train of claim 1, wherein the nominal length is equal to the minimum length plus up to one-third of a difference between the minimum length and the maximum length.
 3. The valve train of claim 2, wherein the nominal length is equal to the minimum length plus one of 3%, 10% and 20% of the difference between the minimum and maximum lengths.
 4. The valve train of claim 1, wherein the at least one coupling component includes a push rod.
 5. The valve train of claim 4, wherein the at least one coupling component further includes a rocker arm.
 6. The valve train of claim 5, wherein the valve includes a valve stem, wherein an end of the valve stem abuts a first end of the rocker arm, wherein a first end of the push rod abuts a second end of the rocker arm, and wherein a second end of the push rod abuts a first end of the hydraulic lifter, a second end of the hydraulic lifter being in contact with the cam.
 7. The valve train of claim 5, wherein the mechanism includes at least one of an adjustment nut and a set screw that can be varied in position so as to vary a position of the rocker arm and thus further vary a position of the push rod, causing the nominal position of the hydraulic lifter to be varied.
 8. The valve train of claim 4, wherein the mechanism includes a device capable of varying a length of the push rod.
 9. The valve train of claim 1, wherein the cam includes an automatic compression release mechanism by which a shape of a perimeter of the cam can be varied.
 10. An internal combustion engine comprising: a crankcase; a crankshaft supported by the crankcase; a camshaft having a cam, wherein the camshaft is supported by the crankcase and is rotationally coupled to the crankshaft so that rotation of the crankshaft causes rotation of the camshaft; a valve; at least one component coupling the valve to the cam, wherein the at least one component includes a hydraulic lifter; and a mechanism for adjusting a nominal position associated with the hydraulic lifter so that the nominal position is closer to a first position at which the hydraulic lifter is at a minimum length than to a second position at which the hydraulic lifter is at a maximum length.
 11. The internal combustion engine of claim 10, wherein the at least one component further includes at least one of a push rod and a rocker arm.
 12. The internal combustion engine of claim 11, wherein the mechanism includes at least one of an adjustment nut and a set screw that is capable of adjusting a position of the rocker arm in relation to the crankcase, which in turn adjusts the nominal position of the hydraulic lifter.
 13. The internal combustion engine of claim 11, wherein the mechanism includes a device that is capable of adjusting a length of the push rod.
 14. The internal combustion engine of claim 10, wherein the cam includes a means for providing automatic compression release functionality.
 15. The internal combustion engine of claim 10, wherein the mechanism adjusts the nominal position to be at no more than one-third of a distance from the first position to the second position.
 16. The internal combustion engine of claim 15, wherein the mechanism adjusts the nominal position to be at one of 10% and 20% of the distance.
 17. A method of configuring a hydraulic lifter of an internal combustion engine, the method comprising: providing a valve train including the hydraulic lifter, wherein the valve train couples a cam of the engine to a valve of the engine at least indirectly by way of the hydraulic lifter; and adjusting at least one component of the valve train to set a nominal length of the hydraulic lifter so that the nominal length is substantially closer to a minimum length of the hydraulic lifter than a maximum length of the hydraulic lifter.
 18. The method of claim 17, wherein the nominal length is set to be equal to the minimum length plus up to one-third of a difference between the minimum length and the maximum length.
 19. The method of claim 18, wherein the nominal length is equal to the minimum length plus one of 3%, 10% and 20% of the difference between the minimum and maximum lengths.
 20. The method of claim 18, further comprising: readjusting the nominal position of the hydraulic lifter at a later time. 